1. Field of the Invention
This invention relates generally to an apparatus for the reading or play-back of signal information recorded on a record medium, and more particularly is directed to improvements in such apparatus of the type in which signal information recorded as variations in a record track on a reflective record medium surface is optically read or played back by projecting a light beam against the record track on the record medium surface for reflection from the latter and detecting the modulation of the reflected light beam resulting from the variations in the record track representing the recorded signal information.
2. Description of the Prior Art
In existing apparatus of the described type, for example, the conventional video disk player, there are employed, in addition to the signal information reading light beam, a tracking servo-control light beam for causing the reading light beam to accurately track or follow the record track which may be spirally formed on a record disk, and a focus servo-control light beam for maintaining focus of the reading light beam on the record disk even when the latter deflects in the direction at right angles to its plane of rotation. Usually, the several light beams are all obtained from a single light source, such as, a laser. In such cases, a single light beam emitted by the light source is split into the several light beams, that is, the reading light beam, tracking servo-control light beam and focus servo-control light beam, by means of a conventional beam splitter so that all of the beams have the same light characteristics. In other words, the conventional beam splitter is merely effective to split the original single light beam into a plurality of light beams which are spatially displaced relative to each other. When the plural light beams are obtained from a single light beam by a conventional beam splitter, and the distances between the plural beams, as reflected from the record medium surface, are made small as is required in the interests of accuracy and of providing a desirably compact signal information reading apparatus, there is considerable leakage of the light beams into each other, that is, it is difficult to individually detect the energy of the light beams as reflected from the record medium surface. Further, under the described conditions, it is difficult to prevent the return of the reflected beams to the laser with the result that full utilization of the laser power cannot be attained and the stability of the laser oscillation is frequently deteriorated.